1. Field of the Invention
The invention relates to tapered triblock copolymers, reinforced materials containing the polymers, and articles made from the reinforced materials.
2. Description of the Related Art
Anionic polymerization is a well-known technique for manufacturing plastics and elastomers. Due to the “living” character of the polymer chains during the anionic polymerization process, anionic polymerization allows for the production of polymers having well-defined polymer blocks and narrow molecular weight distributions. Anionic polymerization has long been used to polymerize conjugated dienes such as butadiene and isoprene and to copolymerize such conjugated dienes with other anionically polymerizable monomers, such as monovinyl aromatics and substituted monovinyl aromatics. Commercial polymers commonly made through the anionic polymerization process include plastics such as polystyrene, elastomers such as polybutadiene, polyisoprene and styrene-diene rubbers, and thermoplastic elastomers such as block copolymers of styrene, butadiene and isoprene with varying sizes and numbers of blocks.
Many commercial applications for polymers prepared by anionic polymerization may be found in the literature. The polymers prepared by anionic polymerization may be useful in their own right as elastomers for tires and other industries, adhesives, sealants and coatings. In addition polymers prepared by anionic polymerization may be used to modify the characteristics of various materials such as asphalt, plastics and rubbers. For example, the polymers prepared by anionic polymerization may be used as compatibilizers and reinforcing agents in asphalt and compatibilizers or tie layers in polymer blends. The polymers prepared by anionic polymerization may be used as impact modifiers, reinforcing agents or viscosity modifiers in plastics used to manufacture molded and extruded goods such as injection molded parts and engineering components, films and fibers.
The polymers prepared by anionic polymerization may be modified in order to improve their characteristics for their intended applications. Many modification routes have been developed over the years. The most common modifications routes include: molecular weight; molecular weight distribution; monomer composition; diene microstructure; monomer sequence length distribution; stereochemistry; monomer addition order and sequencing; chain coupling through reactions of multifunctional species with living anions to synthesize polymers with linear, radial, comb, arm-like, branched or hyper-branched structures; and combinations of the above modifications. More sophisticated modifications routes include: introducing chemical functionalities through end-capping reactions or functional initiators; polymerization with multifunctional initiators to directly synthesize polymers with linear, radial, comb, arm-like, branched or hyper-branched structures; hydrogenation of residual double bonds; and combinations of the above modifications.
Among the polymers prepared by anionic polymerization, tapered diblock copolymers of conjugated diene and monovinyl aromatic monomers have been of long-lasting commercial importance due to its performance in many applications and its unique properties. Special processing characteristics such as high extrudability and excellent flow combined with mechanical properties such as high hardness, low shrinkage and high abrasion resistance, have been a desirable polymer properties balance for many high-productivity applications.
U.S. Patent Application Pub. No. 20030176582, which lists Bening et al. as inventors and is incorporated by reference, was published on Sep. 18, 2003. Paragraphs [0030] to [0035] describe an A-B-C triblock copolymer. Block A is a mono alkenyl arene polymer block. Block B is a controlled distribution copolymer block of at least one conjugated diene and at least one mono alkenyl arene. Block C is a conjugated diene polymer block. U.S. Pat. No. 5,191,024, issued to Shibata et al. on Mar. 2, 1993, and incorporated by reference, provides examples of triblock copolymers. Example 25 describes polymerizing styrene in tetrahydrofuran to make an A block, followed by polymerizing 600 g of 1,3 butadiene with 170 g of styrene to make a block B, and a block C was made by polymerizing 95 g of 1,3 butadiene with 95 g of styrene monomer. Examples 51-54 and comparative example 25 also describe triblock copolymers. U.S. Pat. No. 4,075,285, issued to Tabana et al. on Feb. 21, 1978 and incorporated by reference, describes various multiple-block copolymers that contain a rubber-modified polystyrene block and a styrene-butadiene block copolymer block. One example describes making a triblock copolymer having a first styrene block, a second styrene-butadiene block and a third styrene block. These patent documents are merely several of many documents that describe how materials can be made that have different properties.
However, it is still highly desirable to improve on the balance between processing and mechanical properties for the ultimate performance. It is desirable to further modify tapered block copolymers prepared by anionic polymerization to improve their performance in different applications and improve on properties such as compatibility, miscibility, adhesion or dispersibility in or with other materials when the polymers are included in a physical or reactive blend. For example, many styrene/butadiene-based and styrene/isoprene-based polymers prepared by anionic polymerization are insufficiently compatible and have met with limited success in the reinforcement of asphalt for paving and roofing applications. Although styrene/butadiene-based and styrene/isoprene-based polymers, both linear and non-linear, are widely used in reinforcing asphalt, problems related to the dispersibility of the polymers prepared by anionic polymerization in the asphalt formulations and to the morphology stability of the resulting polymer modified asphalt blends ultimately have a negative effect on the storage and long-term performance of the modified asphalt. Similar problems have arisen in applications where anionically polymerized polymers are used as pressure sensitive adhesives and hot melt adhesives and when the polymers prepared by anionic polymerization are used as impact modifiers in plastics for (co)extrusion or (co)injection molding applications.
Thus, it would be desirable to develop a method for preparing polymers by anionic polymerization to produce modified tapered block copolymers that are more processable, dispersible and compatible with a wide variety of materials and other substrates, including asphalt, adhesive and sealant ingredients, rubber and plastic, and suitable for a broad range of applications. The desired overall performance for an application of the modified tapered block copolymers in blends with the above referred materials and substrates is a balance between maximized processing characteristics such as melt viscosity, extrudability, and flow; increased dispersibility and compatibility to provide higher blend stability; and good elastomeric and thermoplastic properties.